The present invention relates to a method for the loading of nicotine onto cation exchange resins under anhydrous conditions.
Nicotine is a naturally occurring alkaloid that is found in the tobacco plant, Nicotiana tobacum. It finds great use in the pharmaceutical and agricultural industries. In the pharmaceutical industry it is extensively used in smoking cessation formulations. In this use the nicotine can be administered in the form of lozenges, chewing gum, and inhalers.
When nicotine is formulated into chewing gum and lozenges it is first loaded onto a cation exchange resin which has the effect of controlling the release rate of the nicotine during chewing or sucking in the mouth. Such complexes of nicotine with ion exchange resins are the subject of GB1325011. In agriculture it is used as a pesticide; and it is formulated as the nicotine sulfate salt in water, at a 40% concentration.
The typical method for loading substances onto an ion exchange resin is to dissolve an acidic or basic, ionizable substance in water, and then mix it with a suitable ion exchange resin. The substance is absorbed into the resin by the mechanism of ion exchange. See U.S. Pat. No. 2,990,332. The extent of loading will depend on several factors, including the rate of diffusion, the equilibrium constant, temperature, and the presence of other ions. The water is then removed by filtration, and the polymeric complex dried by heating.
The use of non-aqueous solvents as media for ion exchange reactions is known. See, xe2x80x98Ion Exchange Resinsxe2x80x99 by Robert Kunin, p. 310, published by Robert E. Krieger Publishing Co, 1990. However, reactions times are reported to be very long for non-swelling solvents, and the solvents typically used are not optimum for industrial scale because they are flammable, or toxic, or difficult to remove efficiently, or difficult to re-use, or environmentally unacceptable, or high cost.
In the currently used commercial processes to make the polymeric complex of nicotine, nicotine is loaded onto a ground, weakly acidic cationic ion exchange with a methacrylic backbone and carboxylic acid functionality. The loading is performed in a predominantly aqueous system, whereby the nicotine becomes immobilized on the resin by reaction with the carboxylic acid groups. Use of an aqueous system for the loading has the disadvantage that the resulting slurry has to be dewatered and dried. This is currently achieved in a number of different ways, e.g. dewater in a decanter, and then dry in a vacuum dryer; evaporate the water directly from the slurry in a vacuum distillation apparatus; or evaporate the water directly from the slurry using a spray dryer. There are problems associated with each of these methods. The decanter operation is made difficult because the cation exchange resin contains a significant fraction of very fine particles ( less than 40 micron), and wet-cakes from such decanters can still contain  greater than 60% water by weight. The spray dryer and vacuum distillation operations are wasteful of energy because all the water is removed by conversion to water vapor. All of these methods can also lead to particle agglomeration. Avoidance of these problems by using typical organic solvents would be expected to lead to problems of toxicity from residual solvent, safety problems from flammability, and environmental problems from vapor emissions and waste disposal.
Applicants have surprisingly discovered how to load nicotine onto cation exchange resins in an anhydrous system, using a halogenated hydrocarbon solvent and a dry cation exchange resin. By performing the loading operation under such anhydrous conditions all the problems associated with dewatering are eliminated, and the cost of removing the residual water by drying can be replaced with the much lower cost of removing the halogenated hydrocarbon solvent. For example, one embodiment of the present invention uses 1,1,1,2-tetrafluoroethane (TFE). The boiling point of TFE is xe2x88x9226xc2x0 C. It is essentially benign in humans, such that it is approved by the FDA for use as the propellant in inhalers. It has been shown to be non-ozone depleting. It is non-flammable. Use of this particular non aqueous solvent allows very efficient recovery and re-use of the solvent under very mild conditions and eliminates problems of toxicity from residual solvent, safety problems from flammability, and environmental problems from vapor emissions and waste disposal.
The following terms have the following meanings herein:
The terms xe2x80x9cloadedxe2x80x9d and xe2x80x9cloading,xe2x80x9d as used here-in, mean the preparation of a resinate. The amount of loading means the amount of active substance incorporated into the resinate.
The term xe2x80x9cresinate,xe2x80x9d as used herein, means an active substance/ion exchange resin complex.
Further, ion exchange resins are characterized by their capacity to exchange ions. This is expressed as the xe2x80x9cIon Exchange Capacity.xe2x80x9d For cation exchange resins the term used is xe2x80x9cCation Exchange Capacity.xe2x80x9d The ion exchange capacity is measured as the number equivalents of an ion that can be exchanged and can be expressed with reference to the mass of the polymer (herein abbreviated to xe2x80x9cWeight Capacityxe2x80x9d) or its volume (often abbreviated to xe2x80x9cVolume Capacityxe2x80x9d). A frequently used unit for weight capacity is xe2x80x9cmilliequivalents of exchange capacity per gram of dry polymer.xe2x80x9d This is commonly abbreviated to xe2x80x9cmeq/g.xe2x80x9d
Ion exchange resins are manufactured in different forms. These forms can include spherical and non-spherical particles with size in the range of 0.001 mm to 2 mm. The non-spherical particles are frequently manufactured by grinding of the spherical particles. Products made in this way typically have particle size in the range 0.001 mm to 0.2 mm. The spherical particles are frequently known in the art as xe2x80x98Whole Bead.xe2x80x99 The non-spherical particles are frequently known in the art as xe2x80x98Powders.xe2x80x99
The present invention relates to a method for loading nicotine onto cation exchange resins under anhydrous conditions comprising the steps:
a. preparing a nicotine/cation exchange resin/solvent mixture by blending said nicotine and cation exchange resin and said solvent together at a pressure and temperature that maintains said solvent in the liquid state,
b. maintaining said mixture, at a pressure and temperature that maintains said solvent in the liquid state, for 1 second to 48 hrs.,
c. evaporating said solvent from said mixture to obtain a nicotine-loaded resin.
The present invention relates to a method for loading nicotine onto cation exchange resins under anhydrous conditions comprising the steps:
a. preparing a nicotine/cation exchange resin/solvent mixture by blending said nicotine and cation exchange resin and said solvent together at a pressure and temperature that maintains said solvent in the liquid state,
b. maintaining said mixture, at a pressure and temperature that maintains said solvent in the liquid state, for 1 second to 48 hrs.,
c. evaporating said solvent from said mixture to obtain a nicotine-loaded resin.
Ion Exchange resins useful in the practice of the present invention include, but are not limited to, styrenic strongly acidic cation exchange resins with sulfonic or phosphonic acid functionalities having a weight capacity of 0.1 to 8 meq/g, and styrenic weakly acidic cation exchange resins with carboxylic or phenolic acid functionalities having a weight capacity of 0.1 to 8.5 meq/g, and acrylic or methacrylic weakly acidic cation exchange resins with a carboxylic or phenolic acid functionality having a weight capacity of 0.1 to 14 meq/g, that are suitable for human and animal ingestion.
Preferred cationic exchange resins include, but are not limited to, styrenic weakly acidic cation exchange resin with a phenolic functionality with a weight capacity of 0.1 to 8.5 meq/g, a styrenic strongly acidic cation exchange resin with a sulfonic acid functionality with weight capacity of 0.1 to 8 meq/g, or acrylic or methacrylic weakly acidic cation exchange resin with a carboxylic acid functionality with weight capacity of 0.1 to 14 meq/g.
The more preferred cationic exchange resins include, but are not limited to, acrylic or methacrylic weakly acidic cation exchange resins with a carboxylic acid functionality with weight capacity of 0.1 to 14 meq/g.
The most preferred cationic exchange resin is a methacrylic weakly acidic cation exchange resin with a carboxylic acid functionality with weight capacity of 0.1 to 12 meq/g.
Strongly acidic and weakly acidic cation exchange resins useful in this invention are in the acid form or salt form or partial salt form.
Ion exchange resins useful in this invention are in powder or whole bead form.
The preferred ion exchange resins useful in this invention are in powder form.
The ion exchange resins used in the practice of the present invention have between 0% and 20% water.
The preferred ion exchange resins used in the practice of the present invention have between 0% and 10% water.
The most preferred ion exchange resins used in the practice of the present invention have between 0% and 5% water.
Nicotine useful in the practice of the present invention includes, but is not limited to, that derived from the extraction of nicotine from the tobacco plant Nicotiana tobacum. 
The preferred nicotine useful in the practice of the current invention is nicotine that has an assay greater than 90% by weight.
The more preferred nicotine useful in the practice of the current invention is nicotine that has an assay greater than 95% by weight.
The most preferred nicotine useful in the practice of the current invention is nicotine that meets the purity specifications prescribed in the US Pharmacopeia USP24, p1179.
Solvents useful in the practice of the present invention include, but are not limited to, halogenated hydrocarbons, ketones, alcohols, ethers, hydrocarbons, esters, nitrites and mixtures thereof.
The preferred solvents used in the present invention are fluorohydrocarbons with boiling points at atmospheric pressure between 30xc2x0 C. and xe2x88x92100xc2x0 C.
The more preferred solvents are:
trifluoromethane (CF3H);
fluoromethane (CH3F);
difluoromethane (CF2H2);
1,1-difluoroethane (CF2HCH3);
1,1,1-trifluoroethane (CF3CH3);
1,1,1,2-tetrafluroethane (CF3CFH2) (TFE)
pentafluoroethane (CF3CF2H);
1,1,1,2,2-pentafluorpropane (CF3CF2CH3);
1,1,1,2,2,3-hexafluoropropane (CF3CF2CFH2);
1,1,1,2,3,3-hexafluoropropane (CF3CFHCF2H);.
1,1,1,3,3,3-hexafluropropane (CF3CH2CF3);
1,1,2,2,3,3-hexafluoropropane (CF2HCF2CF2H);
1,1,1,2,2,3,3-heptafluoropropane (CF3CF2CF2);
1,1,1,2,3,3,3-heptafluoropropane (CF3CFHCF3);
The most preferred solvent is 1,1,1,2-tetrafluoroethane (TFE)(CF3CFH2).
The solvent is removed from the final mixture either by heating to the boiling point of said solvent and removing it by distillation, or by reducing the pressure, and providing a heat source to maintain the temperature of the solution between room temperature and the atmospheric pressure boiling point of said non aqueous solvent. When said solvent has a boiling point at atmospheric pressure of approximately  less than 0xc2x0 C. it is expected to be removed essentially quantitatively at atmospheric pressure and room temperature. Such solvents can be conveniently recovered and reused by using a compressor and condenser, or a condenser at less than the boiling point of said solvent.
Loading times useful in the present invention are between 1 sec and 48 hours.
The preferred loading times useful in the invention are between 10 minutes and 18 hours.
The most preferred loading times useful in the invention are between 1 hour and 8 hours.
The preferred concentration of the nicotine to solvent useful in the practice of the invention is from 0.01% to 20% by weight of nicotine.
The more preferred concentration of the nicotine to solvent useful in the practice of the invention is from 0.1% to 10% by weight of nicotine.
The most preferred concentration of the nicotine to solvent useful in the practice of the invention is from 0.1% to 2% by weight of nicotine.
Preferably, the loading of nicotine onto the resin in the present invention is 5-100% of the ion exchange capacity of the resin, more preferably it is 10-90% of the ion exchange capacity of the resin, and most preferably it is 15-80% of the ion exchange capacity of the resin.